Certain diseases and disorders of the respiratory tract are known to respond to treatment by the direct application of therapeutic agents. As these agents are most readily available in dry powder form, their application is most conveniently accomplished by inhaling the powdered material through the nose or mouth. This powdered form results in better utilization of the medication, as the drug is deposited at the site where its action is needed; hence, very small doses of the drug are often as efficacious as larger doses administered orally or by injection, with a consequent marked reduction in the incidence of undesired side effects and medication cost. Alternatively, a drug in powder form may be used for the treatment of diseases and disorders other than those of the respiratory system. When the drug is deposited on the large surface areas of the lungs, it may be rapidly absorbed into the blood stream; hence, this method of application may take the place of administration by injection, tablet, or other conventional means.
Dry powder inhalers (DPI's) of the prior art have means for introducing a drug formulation into an air stream. Several inhalation devices useful for dispensing a powder form of medication are known in the prior art. For example, U.S. Pat. Nos. 2,517,482; 3,507,277; 3,518,992; 3,635,219; 3,795,244; 3,807,400; 3,831,606; 3,948,264; and 5,458,135 describe inhalation devices, many of which have means for piercing or removing the top of a capsule containing a powdered medication. Several of these patents disclose propeller means, which aid in dispensing the powder out of the capsule. Other DPI's utilize a vibratory element, such as those described in U.S. Pat. Nos. 5,694,920; 6,026,809; 6,142,146; 6,152,130; 7,080,644 and 7,318,434.
The prior art devices possess several disadvantages. For example, they often require that the user exert considerable effort in inhalation to effect withdrawal of the powder into the inhaled air stream. Thus, their performance often heavily depends on the flow rate generated by the user—a low flow rate may not result in the powder being sufficiently deaggregated, which can cause uncontrolled amounts or clumps of powder being inhaled into the user's mouth, rather than a constant inhalation of controlled amounts of finely dispersed pharmaceutical. This adversely affects the dose delivered to the patient and can lead to inconsistency in the bioavailability of the drug from dose-to-dose due to lack of consistency in the deaggregation process. Consequently, patients that cannot produce sufficiently high flow rates, such as pediatric, elderly, and patients with severely compromised lung function (e.g., COPD), may receive reduced and/or variable doses at the intended site of delivery. Moreover, suction of powder through the pierced holes of a capsule by inhalation often does not withdraw all or even most of the powder out of a capsule, thus causing a waste of the medication. The large energy requirements for driving electromechanical based inhalers typically increase the size of the devices, making them unsuitable for portable use.
Nebulizers provide an alternative mechanism for delivering medication to the respiratory system in a manner that may not require forceful inspiration. However, current nebulization systems are limited by relatively slow drug delivery; for example, some systems require a session of at least 10-20 minutes. This is especially undesirable for patients that regularly use a nebulizer several times per day. Also, nebulizers typically lack portability, are cumbersome to set up, and require a significant amount of cleaning and maintenance, among other drawbacks.
Efficient delivery of inhaled medication is desirable for the success of pulmonary-delivered therapies. One of the most desirable factors in pulmonary delivery from a DPI is a high-quality aerosol, in terms of the aerosol's aerodynamic particle size, and its potential to consistently achieve the desired lung deposition in vivo. The optimal delivery of inhaled medications is hindered in current devices by the need for patients to inhale forcefully while coordinating inspiration with the device, as well as by the physical limitations of the patient. Devices that provide means for deaggregating the powder have not been shown to provide consistent dose delivery or particle size distribution. These problems highlight the significant unmet need for simpler, portable, easier-to-use devices that do not require coordination with forceful inspiration, provide a short duration of administration, and deagglomerate the drug formulation in a manner that ensures a consistent particle size distribution of the delivered dose throughout the life of the device.